The marketplace currently offers two primary types of drill chuck mechanisms for retaining drilling and driving tool bits. The traditional or "incremental" design typically consists of a mechanism that houses three adjustable jaws which protrude at an angle into a bore. An external sleeve is coupled to the jaws via internal gear teeth. When a tool is inserted into the bore, the sleeve is rotated by a user. As the sleeve is rotated in one direction, the jaws are forced towards the center of the bore to clamp a tool bit. When the sleeve is rotated in the opposite direction, the jaws are opened. This chuck style is able to accommodate a variety of tool sizes and shapes, however, changing a tool bit takes time.
It has long been recognized that the ability to quickly change tool bits in the spindle of a power tool is an advantageous feature. Construction workers and carpenters regularly change drill bits in numerous types of construction projects, often when the worker is in a position where it is difficult to change the bit, such as on a ladder. To change a drill bit, the carpenter must loosen the chuck, remove the old bit from the chuck, insert the new bit and tighten the chuck.
A second, more recent approach to chuck design allows for tools to be exchanged in a "quick-change" manner. Examples of quick-change mechanisms such as this are explained in U.S. Pat. Nos. 4,900,202 and 5,013,194, both of which are incorporated by reference herein. Quick-change chucks typically require the use of tools that have shanks that are of a consistent size (typically, 1/4" hex shank), and usually have hexagonal cross sections. This style of chuck does not allow for accommodating a variety of tool shank sizes.
The traditional three-jaw approach accommodates tools with round shanks and a range of different diameters and the more recent "quick-change" chucks allow for switching bits in a timely manner. None of the designs for chucks, however, combine these two features and accommodate the "quick change" style tool shanks as well as the flexibility of accommodating variable shank sizes using an "incremental" approach.